In recent years, a waterproof support comprising a raw paper covered with a polyolefin, such as polyethylene, on both sides has been used by preference as a support for photographic printing paper with the intention of not only preventing processing solutions from penetrating into a photographic printing paper support in developing and fixing steps but also reducing a processing time including washing and drying times.
As for the raw paper, the so-called acidic paper has so far been used. The acidic paper is prepared from paper stock to which an anionic sizing agent, an anionic paper-strength reinforcer and a cheap aluminum salt for fixing these anionic chemicals to pulp are added, thereby being rendered acidic.
Recently, however, neutral paper has prevailed as paper for general use because of its advantages, e.g., in having improved keeping quality, enabling the white water discharged in a paper-making step to be disposed in a closed system, preventing equipments from being corroded, and so on.
In using a raw paper for making a support of photographic printing paper, it is required of the raw paper to be hard sized paper. This is because the support should avoid being invaded by a developer via the cut surfaces thereof in the course of development.
When neutral paper is used as raw paper for a photographic printing paper support, therefore, it becomes necessary to incorporate therein not only an alkylketene dimer having self fixability as sizing agent but also a cationic polyacrylamide as paper strength reinforcer. However, the papermaking in the neutral region (6.0.ltoreq.the pH of paper stock.ltoreq.8.5) is inferior in the drainage on wire cloth to the papermaking in the acidic region (3.5.ltoreq.the pH of paper stock &lt;6.0). Accordingly, the papermaking in the neutral region has a problem of its suffering an increase in drying load. Further, it has drawbacks that the alkylketene dimer used therein as sizing agent is responsible for stains on rolls such as press rolls and tends to render the raw paper surfaces slippery.
Those drawbacks can be mitigated by using a specific cationic polyacrylamide, that is, the cationic polyacrylamide obtained by copolymerizing an acrylamide with cationic monomer(s) and has its molecular weight and cationic value in the respectively specified ranges (as disclosed in JP-A-04-131843, and the term "JP-A" as used herein means an "unexamined published Japanese patent application).
It is also ascertained in the above-cited reference that a further improvement can be brought about by further adding an anionic polyacrylamide in combination with an epoxidized higher fatty acid amide to the foregoing paper stock in the neutral region.
As a result of our further studies of compounds capable of functioning as paper strength reinforcer, it has been found out that when in the process of making a raw paper, (i) the combination of cationic starch and polyamidepolyamine epichlorohydrin, which have so far been thought that they couldn't produce any preferable effect when used independently, is used as a paper strength reinforcer in addition to a sizing agent comprising an epoxidized higher fatty acid amide and/or an alkylketene dimer, (ii) the pH of paper stock is adjusted to the neutral region and (iii) the zeta potential of the paper stock is controlled so as to be in a specified range, the stain troubles in the course of paper-making can be easily prevented from occurring and, what is more, when the raw paper prepared under the foregoing condition is coated with a polyolefin resin on both sides to be made into a photographic printing paper support, the penetration of a developer into the support via the cut surfaces thereof can be considerably reduced. These effects can be further heightened by using a metal salt of carboxymethyl cellulose and/or an acrylamide/diallylamine salt. copolymer, which each have so far been thought to have no favorable effect when used independently, together with the foregoing paper strength reinforcing combination. The present invention has come to be achieved by these findings.